Electroacoustical apparatus



P 1943- J. ANDERSON 2,328,941

ELECTRO -ACOUS TI CAL APPARATUS Filed Feb. 29, 1940 2 Skieets-Sheet 2 E277 V j III mm/1710 II/I/ 1.

I Stwentor 'tional.

Patented Sept. 7, 1943 UNITED STATES 2,328,941 3 ELEomoAooUsTwAL 'ArrARA'rUs Leslie J. Anderson, Westmont. N; J.,' assignor to 1 America, a. corporation Radio Corporation of Delaware Application February 29, 1940, Serial No. 321,537

13 c ims This invention relates to electro-acoustical apparatus, and more particularly to microphonesof the type wherein a movable conductor is mounted for movement in a magnetic fleld in response to either the pressure component, the pressure gradient component, or both said components of a sound wave.

It is well known that microphones of this type which are responsive only to the pressure gradient, or velocity, component of the sound wave are bi-directional, while those responsive to only the pressure component of the sound wave are non-direction. By suitably combining the two, as disclosed, for example, iny'the reissue patent to Olson and Weinberger; No. 19,- 115, a microphone is obtained which is unidirec- Under varying circumstances, it is'desirabl to employ one or the other of these types of microphones, and the primary object of my pres-' ent invention is to provide a single microphone as aforesaid which may be readily adjusted to operate either as a unidirectional microphone, a bidirectional microphone or a non-directional microphone.

More particularly, it is an object of my present invention to provide a novel microphone of the type set forth which may be readily adjusted to operate either as a microphone responsive to the pressure gradient component of the soundwave, a microphone responsive to the pressure component of the sound wave, or a microphone which is responsive to both said components.

Another object of my present invention is to provide an improved microphone as abovedescribed which is simple in construction, which is comprised of a minimum number of parts, and

which is highly efflci nt in operation.

According to one form of my invention, I mount in the casing which houses the ribbon elements or other moving conductors of the microphone a terminal plate to which the ribbons are connected and also connect thereto the primary winding of a suitable transformer which is also housed within said casing. The secondary winding of this transformer is provided with a suitable tap and this winding and its tap are connected to other terminals on said terminal plate. Rotatably mounted on the casing of the microphone is an annular control member provided with a pair'of sliders adapted to bridge certain of said terminals, depending upon the position of the control or ring member on the casing, and the arrangement is such that, in one position, the velocity section of the ribbon is short circuited and the pressure section of the f ribbon is connected to the primary winding of the transformer with the whole secondary winding 2 operative. In another position of the ring member, the pressure'section of the ribbon is short circuited andthe velocity section is connected to I the primary winding of. the transformer, the whole secondary winding again being operative. Inthe third position ofthe ringmember, both the velocity section and the pressure sectionof the ribbon-are connected to the primary winding of'thfe transformer, and only'a portion of" the secondary windingis rendered operative through the; tapped-connection thereto. ,In way, the outputimpedanceof the microphone}; looking lnto the secondary winding'of the transformer is always constant regardless of which" of theribbon sections maybe connected to the 'primary winding of the transformer.

-l'.n anotherform of my invention, instead of; usingthe annular control member, or ring mam-'31: her, I mount'the transformer in 'a rotatable hou's q ing'at the bottom of the microphone casingiand; provide the. transformer housing with a 'termi nal plateto-which' its windings-are connected,- the primary winding of the transformer, in'this form of myinvention being tapped; By rotating-f; the aforesaid rotatable housing to anyoneof three predetermined positions, suitable connection may be made between the ribbon sections of the movableconductor-and the primary winding" of the transformer such that either thevelocity section alone is connected to the primary wind-' 1, ing through the tapped connection thereto,, th'e pressure section alone is connected to the pri-'-.-. marywinding ofthe transformer, also through said tapped-connection, or both said sections'are connected to the whole primary winding. In)

order to maintain a constant output impedance,

the secondary winding of the transformer may be suitably controlled by external switching'means" to shift the transformer turn ratio depending V upon the -connections .to the primary winding; The novel features that I consider characteristic of my invention are set forth with particu- I larity in the appendedclaims. 'The invention'ite self, however, both as to its organization and method of operation, as well as additional objects 1- 4 and advantages thereof, will best be understood from the 'followingdescriptio'n of two embodi ments thereof, when read in connection withthe accompanying drawings inwhich v Figure 1 is a front elevation of one form of my invention, a

Figure 2 is an enlarged sectional view thereof taken along the line 11-11 of Fig. 1, .Figure 3 is a sectional view taken along-the line III-III of Fig. 2, 4

Figure 4 is a sectional view taken along -the line IV-IV of Fig. 3, I

. Figure 5 is a circuit diagram showing the connections of the vibratile conductor of the microphone and of the transformer to the terminal plate, M V

Figure 6 is a detailed sectional view. showing the cooperation of one of the sliders or bridging elements on the control member of this form of my invention with terminals on the terminal plate,

. Figure 7 is a fragmentary sectional view ofanother form of my invention,

Figure 8 is a sectional view taken along the line VIII-VIII of Fig. 7,

Figure 9 is asectional view along the line IX- IX of Fig. '7,

Figure 10 is a wiring diagram showing the f connections of the movable conductor'to theterminal plate of this form of my invention, and

Figure 11 is-a wiring diagram showing the con.-

nections to the transformer windings.

Referring more particularly to the drawings,

,wherein similar reference characters designate corresponding parts throughout, I have shown, in Fig. 1, a yoke member I upon which is swivelled a casing 3 within which is mounted a movable conductor 5, such as a crimped ribbon mounted for vibration in the air gap of a suitable magnetic structure, all in well known manner. The conductor 5 may be-comprised of two separate ribbons or of asingle ribbon clamped at its center so as to provide the serially connected ribbon sections V and P, the section V being accessible on both sides by sound waves and therefore responsive to the pressure gradient compo-. nent of the sound wave, and the pressure section T P having'a suitable pipe therebehindias shown for example in the above identified Olson et al.

terminals A-B arebridg'ed, whether the terminals'-BC are bridged. or whether the terminals A,BandCare leftopen.

The secondary winding of the transformer l is provided with a tap 8b which divides the sec-'- ondary winding into two sections 90 and 9d, the tap 9b. being connectedby alead 23 to the terminalstrip D. The terminal strips E. anclG are bridged by a lead 25, thestrip E being connected to one side of a suitable power line through a lead 21. The terminal end of the secondary winding section 90 is connected to'the terminal strip F through a lead '29, and the terminal end of the secondary winding portion 9d is connected to the" other side of the power line by means of 'alead 3|,a shield 33 around the leadsZl and 3 I being grounded to the casing of the transformer] by means of a lead 35. 1 i v From the foregoing, it will be obvious that when the terminal 'strips D and E 'arebridged, the secondary'winding portion 9d is connected to the line through the lead 21,- terminal strip terminal strip D, lead 2:, and lead 31'. the

secondar winding portion 80 remaining open circuited. On the other hand, whenthetermi 118.1 strips E and F are bridged or the terminal strips F and G are bridged, both secondary winding portions 9c and 9d are connected to ,theline,

in the former case through the lead :1,- terminal reissue patent) whereby it is responsive to the pressure component of the sound wave.

the lower portion of the casing 3, there is ounted aterminalplate 'lprovided with a plurality of spring terminal members A, B, C, D, E,

F and G. a suitable coupling transformer 9 being secured to the terminal plate 1, as by means of screws or the like II. The common and of the ribbon sections V and P is connected through a lead l3 to the terminal strip B. The other end of the ribbon section P is connected through a lead I! to the terminal strip A, and the other end of the ribbon section V is connected through a'lead II to the terminal strip 0, the primary winding 91; of the transformer 8 being connected through leads I8 and 2 l, respectively. to the terminal strips A and C. It will thus be seen that i the whole ribbon or conductor 5 is connected in series with the primary winding ta of the trans former and that, by-bridging either the terminals A and B, or B and C, either the pressure section P will'be short circuited; or the velocity ".-'section V will be short circuited. depending upon which terminals are bridged. Accordingly, it is 1 possible to adjust the microphoneso that either the voltage generated by the section V will be appliedto the primary winding 9a, the voltage gen.

' erated by the section B will be applied to the primary-winding 9a. or the sum of the voltages generated by'.-the serially connected sections V and P will be applied to the primary winding 9a, depending, respectively, upon whether the strip E, terminal strip F,'lead 29-, and lead M:- and in the latter case through the lead'il," lead G, terminal strip F, lead 20- 25, terminal strip and lead 31.

For efl'ecting the various connections set forth above, I provide on the casing 3a rotatable control member 31 in the form of an'annulus or ring which is connected to a second ring 39 or insulat-T ing material by means ofaplurality of screws or the like 4| which pass through a like number which is adapted to cooperate with a pluralityoi V-shaped notches 41 in a plate 48 secured to the casing of the transformer 9, the detent I and the notches 41 cooperating to releasably lock the ring members 31 and tion. v v

The control or. ring member" 31' is free to be moved circurnferentially on thecasing Swithin the limits ermitted-by the slots ea. When the control member 31 is moved to a position such that the bridge member S1 is out of contact with the terminal strips A, B and .C, and the bridge strips D and 12,. then both of the ribbon sectionsV and P retain operative connection-with the primary winding. 9a. of the transformer and .onLv the secondary winding portion 9d is connected; to the line, as

.the microphone is set for unidirectional operation; If the control member above described. Thus,

311s moved to a posiflon, such. that the bridge member 81 bridges: the terminal strips A and B l and the bridge member 82. bridges the terminal strips E and F, then the pressure section P oftheribbon 5. becomes short circuited and inoperative to apply voltages to the primary winding jsa,

leaving only thevelocity section Voperative for this purpose. the same time, the secondary B and C, and the member B:

39 j in adjusted post 1 M. When it is desired to operate the microphone winding portions 90 and 9d are both connected to the line, and the microphone is conditioned to have a bidirectional characteristic. Similarly, if the control member 31 is moved to a position such that the bridge member S1 bridges the terminal strips B and C and the bridge member S2 bridges the terminal strips F and G, the velocity section V of the ribbon 5 becomes short circuited, both of'the secondary winding portions to and 911 become connected to the line as above described, and only the pressure section P is operative to apply voltages developed thereby. Hence, in the latter case, the microphone is conditioned to be responsive only to the pressure component of a sound wave and has a non-directional characteristic.

To facilitate ascertaining at a glance the operating condition of the microphone at any time, the ring member 37 may have applied thereto a series of indicia 5i, 53 and 55. These are preferably, and respectively, curves simulating the cardioid characteristicof the unidirectional microphone, the non-directional characteristic of the pressure microphone, and the bidirectional characteristic of the velocity microphone, and they may be further differentiated by coloring each of them difierently (for example, blue, red, and green), as indicated in Fig. 1. These, or any other similar indicia, may cooperate with a pointer 5'! on the casing 3 and will be so related thereto that the characteristic appearing under the pointer readily indicates the operating condition of the microphone. I

In Figs. 7 to 11, there is shown another modification of my invention wherein the transformer 9 is housed within a housing 59 to which it is" secured for movement therewith as a unit, as by means of screws 6! or the like. The housing 59 is formed with an upstanding flange 63 which is confined between a shoulder 55 formed on the casing 3 and an annular member 61 of L-shaped cross section which is secured to the casing 3 by the screws 69. The housing 59 is free to rotate in the ring member 51 and the casing 3, and preferably rides on antifriction bearings ii.

The terminal plate "I of this form of my invention is provided with a plurality of spring terminal strips K1, K2, L and M, the terminal end of the velocity section of the ribbon 5 being connected to the terminal strip L by means of a lead as a bidirectional, or velocity, microphone, the transformer housing 59 and the transformer 9 are turned to a position where the terminal T is connected to the terminal strip L and the terminal N is connected to the terminal strip K1, in which case the velocity section V of the ribbon 5 becomes connected to the portion Si of the primary winding of the transformer through the leads i3, 79 and ii. To set themicrophone for operation as a pressure, or nondirectional, microphone, the housing 59 and transformer 9 are turned to a position such that the terminal member T is connected to the terminal strip K2 and the terminal N is connected to the terminal strip M. In such case, the pressure section P of the ribbon 5 is connected to the portion SI of the pri-- terminal strip L. ,In such case, it is obvious that the full primary winding becomes connected to the whole ribbon 5 through the leads i3 and 15. In any case, regardless of the relation of the terminal membersN, O and T with respect tothe terminal strips K1', K2, L and M when there is a connection between them, the output impedance of the transformer 9 will always remain the same because the tap 9e isso chosen as to maintain the proper number of turns in the primary winding when only either the pressure section P or the velocity section V is connected thereto. As in the case of the first described modification of my in- .vention, the housing 59 may be provided with the curves or other suitable indicia 5|, 53, 55 to indicate the operating condition of the microphone.

From the foregoing description, it will be obvious' to those skilled in the art that I have pro-- vided a novel microphone switching arrange-- 'ment by means of which the selected operating condition for the microphone may be quickly and easily obtained. Although I have shown and described. but two embodiments of my invention,

. it will be obvious to those skilled in the art that 113, the terminal end of the pressure section P of the ribbon 5 being connected to the terminal strip M by a lead 15, and the common endsof the ribbon sections V and P being connected to theterminal strips K1 and K2, respectively, by the common lead 71 and the leads 79 and 81. The casing of the transformer Q is also provided with a terminal plate 83 on which are the three terminal strips N, O and T. The primary winding of the transformer 9 in this form of my invention has a tape 9e which divides the primary winding into the portons 91 and 99. The tap lie of the primary winding is connected to the terminal strip T on the plate 83, the terminal end of the primary winding portion 9 is connectedto the terminal strip N, and the terminal end of the primary winding portion'sg is connected to the terminal member 0.

The adjustment of this form of my invention is very similar to that described above in connection with the modification shown in Figs. '1 to 6'. All that is necessary is to turn the transformer housing 59 one way or the other to obtain the desired connections between the terminal members N, O and T and the terminal strips K1, m, L and many other modifications, as well as changes in those described, are possible. For example, to

facilitate detecting at a distance the particular understood that I do not wish my invention to be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims. 4

I claim as my invention:

1. In a sound pick-up system, the combination of a casing, a pair of electro-dynamic translating units therein each including a vibratile element, one of said elements being responsive to the pressure gradient component ahd the other to the pressure component'of a sound wave, said elements being adapted to develop voltages upon' vibration thereof in response to said components, a coupling transformer including a primary winding, and control means movably mounted on said casing for selectively connecting to said primary winding either one or both of said elements at will, said control means including means for selecting and rendering effective predetermined portions of the secondary winding of said transformer in accordance with the selected one or both of said elements connected to said primary winding.

2. In a sound pick-up system, the combination of a casing, a pair of electro-dynamic translating units therein each including a vibratile element, one of said elements being responsive to the pressure gradient component and the other to the pressure component of a sound wave, said elements being adapted to develop voltages upon vibration thereof in response to said components, a terminal plate in said casing, a plurality of terminals on said plate, a coupling transformer, said elements and the primary winding of said transformer being electrically connected to said terminals, and control means movably mounted on said casing for selectively coupling either one or both of said elements to said primary winding at will whereby to apply said voltages to said transformer.

3. The invention set forth in claim 2 characterized in that said control means comprises an annular member surrounding said casing and slidably mounted thereon.

4. The invention set forth in claim 2 characterized in that said control means comprises an annular member surrounding said casing and slidably mounted thereon, and characterized further by the addition of one or more sliders carried by said member and adapted to coact with said terminals upon moving said member to predetermined positions to efiect connection between the selected one or both of said elements and said primary winding.

5. The invention set forth in claim 2 characterized in that said transformer is provided with a tapped secondary winding, characterized further in that said secondary winding and the tap thereon are connected to certain of said terminals, and characterized still further in that said control means includes a slider adapted to bridge certain of said last named terminals in pairs, said terminals and said slider being so arranged that when either of said elements alone is selected for operation, said slider is effective to render the whole secondary winding of said transformer operative, and when both. said elements are selected for joint operation, said slider is effective to render only a portion of said secondary winding operative.

6. In a sound pick-up system, the combina= tion of a casing having a reference indicium thereon, a pair of electro-dynamic translating units therein each including a vibratile element,

one of said elements being responsive to the pressure gradient component and the other to the pressure component of a. sound wave, said elements being adapted to develop voltages upon vibration thereof in response to said components, a coupling transformer, control means movably mounted on said casing for selectively connecting to said transformer either one or both of said elements at will, and separate indicia comple-' 8. The invention set forth in claim 6 characterized in that said indicia comprise curves simulating the directional characteristics of said elements when acting either singly or jointly, and characterized in that each of said curves is differently colored.

9. In a microphone having a casing within which is carried a vibratile element adapted to be operated in response to either the pressure gradient component of a sound wave, the pressure component of a sound wave, or both said components, control means including a ring member rotatably mounted on said casing for selectively adjusting the microphone to any one of said operating. conditions at will, and means associated with said first ,named'means for indicating the operating condition of the microphone, said indicating means comprising a plurality of curves each simulating the directional characteristics of the microphone corresponding to a. different operating condition thereof and a pointer on said casing for cooperation with said curves.

10. In a sound pick-up system, the combination of a casing, a pair of electro-dynamic translating units therein each including a vibratile element, one of said elements being responsive to the pressure gradient component and the other to the pressure component of a sound wave, 7

said elements being adapted to develop voltages upon vibration thereof in response to said components, a coupling transformer including a primary' winding, and control means including a housing movably mounted on said casing for selectively connecting to said primary winding either one or both of said elements at will, said transformer being housed within said housing and being movable therewith as a unit.

11. In a sound pick-up system, the combination of a casing, a pair of electro-dynamic transla'ting units therein each including a vibratile element, one of said elements being responsive to the pressure gradient component and the other to a pressure component of a sound wave, said elements being adapted to develop voltages. upon vibration thereof in response to said components, a couplin transformer including a. primary winding, and control means including a.

housing rotatably mounted on said casing for selectively connecting to said primary winding either one or both of said elements at will, said transformer being housed within, said housing and being movable therewith as a unit, and said control means also including means associated with said primary winding for selecting and rendering effective either only a portion of said primary winding or the whole of said pri-.- mary winding in accordance with the selected one or both of said elements connected to said primary winding.

12. In a sound pick-up system, the combine-e tion of a casing, a pair of vibratile elements therein one of which is responsive to the pressure gradient component and the other to the pressure component of a sound wave, said elements being adapted to develop voltages upon vibration thereof in response to said'components, a termi nal plate in said casing, a plurality of terminal strips on said plate, said elements having connection with said terminal strips, a housing rotatably carriedby said casing, an output transformer'housed within said housing and secured thereto for movement with said housing as a unit, said transformer including a. tapped primary winding, a second terminal plate on said transformer, and a plurality of terminals on said second named plate, said primary winding and the tap thereon being connected to said last named terminals, and said last named terminals being adapted to coact with said terminal strips for coupling either one or the other of said elements to a portion of said primary winding through said tap, or both said elements to the whole primary winding, depending upon the position of said transformer and said housing on said casing.

13. In a microphone having a casing within which is carried a vibratile element adapted to be operated in response to either the pressure gradient component of a sound wave, the pressure component of a sound wave, or both components, control means including a member rotatably mounted on said casing for selectively adjusting said microphone to any one 0f--sa.id operating conditions at will, and means exterior of said casing associated with said first named means for indicating the operating condition of the microphone.

LESLIE J. ANDERSON. 

